(1) Field of the Invention
The present invention relates to a resin composition markedly improved, particularly, in tensile elongation and multi-axial impact strength as well as Izod impact strength while retaining flowability and heat resistance, and further relates to injection moldings made from the resin composition.
(2) Description of the Related Art
A polyphenylene ether has been extensively used because of superiority in its mechanical properties, electrical properties and heat resistance and further superiority in its dimensional stability. However, polyphenylene ether has a serious defect that it is inferior in oil resistance and molding processability when used singly. In order to dissolve the defect, JP-B-45-997 proposes a technique, wherein a polyamide is blended with polyphenylene ether. At present, such a material has come to be extensively used for various applications.
A technique of adding an impact improving material to a polymer alloy comprising a polyphenylene ether and a polyamide in order to impart impact resistance is disclosed in U.S. Pat. No. 4,315,086. Examples of the impact improving material disclosed therein include di-block copolymers or tri-block copolymers of ethylene propylene rubber, SBR, polybutadiene or polystyrene-diene rubber or partial hydrides thereof.
JP-A-2-58563 discloses a technique, wherein two kinds of elastomers, namely, an ABA type tri-block copolymer and an AB type di-block copolymer are blended with each other, to improve impact resistance.
Further, JP-A-6-240130 discloses a technique, wherein two or more block copolymers having different weight ratios of an aromatic vinyl compound block are blended, to improve molding processability, mechanical properties and heat resistance.
In recent years, compositions comprising the polyamide/polyphenylene ether alloy have been used for the applications, such as a relay block, which is one of the car electrical device parts, or for doors and fenders which are exterior trim parts of cars. In these applications, it is required to particularly enhance multi-axial impact strength, such as falling weight impact strength, among impact strengths. The improvement of the multi-axial impact strength is extremely difficult because this must be achieved while substantially retaining other important properties such as flowability and heat resistance.
WO 02/094936 discloses a technique wherein deterioration of surface appearance and generation of black spots at the time of production can be inhibited while retaining Izod impact strength after heat exposure by using more than one block copolymers different in molecular weight.
Hitherto, impact strength has generally been evaluated by the method called shock fracture toughness, such as (notched) Izod impact test. This is an impact test under mechanical conditions which are severe for materials or articles, and the resulting values do not necessarily show the practical impact strength of the materials or articles. Rather, as described in “Impact Resistance of Plastics” (written by Ikuo Narusawa, published from Sigma Publishing Co., p.1-4), tensile tests or multi-axial impact tests which measure responses with reflecting as much as possible the properties of materials without notching are often regarded to correspond well to the practical impact strength.
According to the above-mentioned conventional techniques, these problems cannot sufficiently be solved. With the expansion of applications, it has been desired to improve impact strength, corresponding to car crash or falling of containers, particularly, multi-axial impact strength, while maintaining flowability and heat resistance.
The object of the present invention is to provide a thermoplastic resin composition improved in impact characteristics corresponding to car crash or falling of containers, particularly, tensile elongation and multi-axial impact strength, while maintaining flowability and heat resistance of polyamide/polyphenylene ether alloys, and further to provide moldings made from the composition.